package com.eatme.core.hash;

import java.util.TreeMap;

/**
 * V2则行家动态扩容
 */
public class HashTableV2<K,V> {

    private static  final int upperTol = 10;

    private  static final  int lowerTol = 2;

    private static final int initCapacity = 7;

    private TreeMap<K,V>[] hashtable;

    private int M;

    private int size;

    public HashTableV2(int M) {
        this.M =M;
        size = 0;
        hashtable = new TreeMap[M];
        for (int i = 0; i < M; i++)
            hashtable[i] = new TreeMap<>();
    }

    public HashTableV2() {
        this(initCapacity);
    }

    private int hash(K key) {
        return (key.hashCode() & 0x7fffffff) % M;
    }

    public int getSize() {
        return size;
    }

    public void add(K key,V value) {
        TreeMap<K,V> map = hashtable[hash(key)];
        if (map.containsKey(key))
            map.put(key,value);
        else {
            map.put(key, value);
            size++;
            if (size >= upperTol*M)
                resize(2*M);
        }
    }

    public V remove(K key) {
        TreeMap<K,V> map = hashtable[hash(key)];
        V ret = null;
        if (map.containsKey(key)) {
            ret = map.remove(key);
            size--;
            if (size<lowerTol*M&&M/2>=initCapacity)
                resize(M/2);
        }
        return ret;
    }

    public void set(K key,V value) {
        TreeMap<K,V> map =hashtable[hash(key)];
        if (!map.containsKey(key))
            throw new IllegalArgumentException(key + "doesn`t exist!");
        map.put(key,value);
    }

    public boolean contains(K key) {
        return hashtable[hash(key)].containsKey(key);
    }

    public V get(K key) {
        return hashtable[hash(key)].get(key);
    }

    private void resize(int newM) {
        TreeMap<K,V>[] newHashTable = new TreeMap[newM];
        for (int i = 0; i < newM; i++)
            newHashTable[i] = new TreeMap<>();
        int oldM = M;
        this.M = newM;
        for (int i = 0; i < oldM; i++) {
            TreeMap<K,V> map = hashtable[i];
            for (K key: map.keySet())
                newHashTable[hash(key)].put(key,map.get(key));
        }
        this.hashtable = newHashTable;
    }


}
